Various vehicle-based communication systems allow vehicles to communicate with other devices inside or outside of the vehicle. For example, a Bluetooth system may enable communication between the vehicle and the driver's mobile phone. Telematics systems (e.g., on-board diagnostics (OBD) systems installed within vehicles) may be configured to access vehicle computers and sensor data and transmit the data to a display within the vehicle, a personal computer or mobile device, or to a centralized data processing system. Data obtained from OBD systems has been used for a variety of purposes, including maintenance, diagnosis, and analysis. Additionally, vehicle-to-vehicle (V2V) communication systems can be used to provide drivers with safety warnings and collision alerts based on data received from other nearby vehicles and/or to evaluate other drivers on the road.